OBJECTIVES To investigate the interrelationships among physiology, behavior, and reproductive output. Paternity analysis based on DNA fingerprinting and STR marker typing continues to expand our longitudinal data base on the monkeys at Cayo Santiago and at Sabana Seca. Due to the occurrence of non-troop males siring offspring on the island of Cayo Santiago, establishing sirehood presents more difficulties than in the enclosed group at Sabana Seca. Our work has enabled us to more directly compare male and female reproductive patterns in the two main study troops. The key results emerging from our recent analyses are (a) age at first reproduction in males is associated with body size, and body size when a young adult is correlated with body size as an infant; (2) dominance rank influenced body weight of male infants, but not female infants; (3) primiparous females bearing sons experienced reproductive costs in that sons were less likely to survive than daughters, and subsequent reproduction was delayed if son was successfully reared; (4) female assistance to peers is associated more wit h familiarity than with degree of genetic relationship. RESULTS We have found that infant growth trajectories in males can predict reproductive success as young adults among rhesus monkeys. FUTURE DIRECTIONS We plan to continue to monitor and analyze the genetic data in order to establish a more complete picture of the variance in male reproduction, the potential for paternal effects on various traits, and age-specific rates of reproduction in rhesus macaques residing on Cayo Santiago. KEY WORDS growth, development, hormones, puberty, dominance rank, paternity FUNDING NIH P5D RR03640 PUBLICATIONS Bercovitch, F. B., M. R. Lebron, H. S. Martinez, and M. J. Kessler. 1998. Primigravidity, body weight, and costs of rearing first offspring in rhesus macaques. Amer. J. Primatol. 46 135-144 [J]. Nurnberg, P., U. Sauermann, M. Kayser, C. Lanfer, E. Manz, A. Widdig, J. D. Berard, F. B. Bercovitch, M. Kessler, J. Schmidtke, and M. Krawczak. 1998. Paternity assessment in rhesus macaques (Macaca mulatta) Multilocus DNA fingerprinting and PCR marker typing. Amer. J. Primatol. 44 1-18 [J].